The present invention relates to a manifold air pressure sensor for a vehicle, and more particularly, to a method and a system for diagnosing malfunctions of the manifold air pressure sensor, based on an estimate of manifold air pressure.
Generally, an amount of fuel injected into a combustion chamber of a cylinder is determined based on mass air flow. In order to detect mass air flow, a mass air flow sensor (hereinafter referred to as a MAF sensor) or a manifold air pressure sensor (hereinafter referred to as a MAP sensor) is utilized.
The MAF sensor directly detects the mass air flow and provides a signal based on the detected mass air flow to an engine control unit. When a MAP sensor is utilized to ascertain the mass air flow, the engine control unit generally determines the mass air flow from the manifold air pressure detected by the MAP sensor, and inlet air temperature.
Therefore, when the mass air flow is to be ascertained based on a signal of the MAP sensor, the mass air flow cannot be determined if there are malfunctions of the MAP sensor. In this case, the engine may not operate optimally, and it becomes difficult to start the engine or obtain high engine torque. Further, the air/fuel ratio cannot be controlled and large amounts of emission gases are exhausted.
For these reasons it is important to diagnose malfunctions of the MAP sensor. But, diagnosing methods are typically performed based only on whether the signal of the MAP sensor is within a predetermined range. Thus, when the signal of the MAP sensor is fixed at a value between the upper threshold and the lower threshold, or the output of the MAP sensor is distorted by an electrical short of an output line of the MAP sensor, the conventional method cannot detect problems with the MAP sensor. Furthermore, during a malfunction of the MAP sensor, the manifold air pressure is estimated based on a current engine speed and a current throttle position, which does not allow the engine to be operated optimally. Therefore, there is a need in the art for an improved method and system for diagnosing a MAP sensor.
In a preferred embodiment of the present invention, MAP (Manifold Air Pressure) sensor diagnostic method comprises: determining whether a MAP sensor signal is within a predetermined range; calculating an intake manifold air pressure based on one or more engine operating parameters; determining whether a difference between a sensed intake manifold air pressure indicated by the MAP sensor signal and the calculated intake manifold air pressure is less than a predetermined value, if it is determined that the MAP sensor signal is within the predetermined range; and selecting the calculated intake manifold air pressure as an actual intake manifold air pressure if the MAP sensor signal is not within the predetermined range, or if the difference between the sensed intake manifold air pressure and the calculated intake manifold air pressure is not less than the predetermined value.
Preferably, a first error counter is increased if it is determined that the MAP sensor signal is not within the predetermined range, and the calculated intake manifold air pressure is determined as the actual intake manifold air pressure if the first error counter is greater than a predetermined value.
It is preferable that a second error counter is increased if it is determined that the difference between the sensed intake manifold air pressure and the calculated intake manifold air pressure is not less than a predetermined value, and the calculated intake manifold air pressure is determined as the actual intake manifold air pressure if the second error counter is greater than a predetermined value.
Preferably, the determining whether a difference between the sensed intake manifold air pressure and the calculated intake manifold air pressure is less than a predetermined value is performed if a throttle position sensor, a camshaft position sensor, and an intake air temperature sensor operate normally.
It is also preferable that the determining whether a difference between the sensed intake manifold air pressure and the calculated intake manifold air pressure is less than a predetermined value is performed if an engine speed is lower than a predetermined speed.
It is further preferable that the determining whether a difference between a sensed intake manifold air pressure and the calculated intake manifold air pressure is less than a predetermined value is performed if a rate of change of a throttle position is less than a predetermined rate.
The one or more engine operating parameters comprise an engine speed, a throttle position, an atmospheric pressure, and an intake air temperature.
In a further preferred embodiment of the present invention, the calculating comprises: calculating a raw air flow drawn into an intake manifold; calculating an adjusted air flow drawn into an intake manifold through an adjustment of the calculated raw air flow; calculating a pressure change based on the calculated adjusted air flow; and calculating the intake manifold air pressure based on the calculated pressure change.
Preferably, the raw air flow is calculated as a sum of a basic air flow passing through a throttle body according to an engine speed and a throttle position, an air flow passing through an idle speed actuator, and a leakage air flow.
It is preferable that the adjustment is performed by multiplying the raw air flow by an air temperature coefficient and a pressure ratio coefficient.
Preferably, the air temperature coefficient Corr_Temp is calculated according to the following equation:   Corr_Temp  =                    T        0                              T          0                +        Tin            
where T0 is a predetermined reference temperature and Tin is a current intake air temperature.
It is also preferable that the pressure ratio coefficient Corr_RPRESS is determined according to the following equation:   Corr_RPRESS  =                              2          ⁢          k                          k          -          1                    ⁢      Pth_in      ⁢              {                              Pth_in            ⁢                                          (                                                      Pin_mod                    ⁢                    _old                                    Pth_in                                )                                            2                k                                              -                                    (                                                Pin_mod                  ⁢                  _old                                Pth_in                            )                                                      k                +                1                            k                                      }            
where Pth_in is a pressure before a throttle plate, Pth_mod_old is a previously calculated intake manifold air pressure, and k is a specific heat ratio.
Preferably, the pressure change (delta_P) is calculated according to the following equation:   delta_P  =                    (                              m_th            ⁢            _in                    -                      m_cylinder            ⁢            _old                          )            xc3x97      R      xc3x97      Tin        Vs  
where m_th_in is the adjusted air flow drawn into the intake manifold, m_cylinder_old is a previous adjusted air flow drawn into a cylinder, Tin is an intake air temperature, Vs is a volume of the intake manifold, and R is a gas constant.
Preferably, method further comprises calculating an air flow drawn into the cylinder based on the calculated intake manifold air pressure, a residual gas pressure in the cylinder, and a predetermined coefficient. The residual gas pressure and the predetermined coefficient can be determined based on an engine speed.
In another preferred embodiment of the present invention, the Manifold Air Pressure (MAP) sensor diagnostic system comprises a MAP sensor and a control unit. The MAP sensor detects an intake manifold air pressure and generates a signal indicative of the detected pressure. The control unit diagnoses malfunctions of the MAP sensor based on one or more engine operating parameters and the MAP sensor signal, the control unit being programmed to perform a control method comprising: determining whether a MAP sensor signal is within a predetermined range; calculating an intake manifold air pressure based on one or more engine operating parameters; determining whether a difference between a sensed intake manifold air pressure indicated by the MAP sensor output signal and the calculated intake manifold air pressure is less than a predetermined value if it is determined that the MAP sensor signal is within the predetermined range; and selecting the calculated intake manifold air pressure as an actual intake manifold air pressure if the MAP sensor is not within the predetermined range, or if the difference between the sensed intake manifold air pressure and the calculated intake manifold air pressure is not less than the predetermined value.